“Oh in Ohio” is a riotously funny comedy on sexual dysfunction and the toll it takes on married life. Lead with two terrific performances by Parker Posey and Paul Rudd, the material sways back and forth through broad comedy, but it almost always hits the mark. Trouble surfaces late in the game when the filmmakers have no idea how to end the film, but the spirit of the material shines all the way through.

Priscilla (Parker Posey) and Jack (Paul Rudd) are a married couple reaching the breaking point of their ten-year union. Jack’s inability to please Priscilla in the bedroom sends him out of the house and into the arms of a comforting high school student (Mischa Barton), while Priscilla decides to confront her frigidity, heading off on an escapade to explore her sexual dysfunction, meeting an unlikely partner (Danny DeVito) who knows exactly how to please her in the process.

Somewhere in the middle “Oh in Ohio” goes from being an insightful, hilarious bawdy comedy to an inert puddle of characters and ideas. It’s upsetting to see first-time director Billy Kent completely unable to put his film back on track after such a strong start; however, what’s here is good quality material, looking to explore marital and comedic areas where few dare to tread.

“Ohio” is complicated material, sure to make some couples in the audience tense up to a point of discomfort. Screenwriter Adam Wierzbianski softens the blow some by shaping the material into a broad comedy, with a dash of acerbic dialog here and sprinkle of slapstick there. The first hour of “Ohio” mines the theme of sexual dysfunction nearly perfectly, embracing the prickly confrontation between the leads and their spiraling exhaustion with the marriage.

With Jack finally seizing his sexual heat again through a consenting 18 year-old and Priscilla learning the miracles that can be found with a vibrator, “Ohio” is lucky to have such two wonderful leads to assist the goofy, sexually charged moments of the screenplay.

Paul Rudd is at his best when playing depressed nonchalance, and his initial scenes of frustration and reckless verbal punches are golden. Parker Posey has the more emotionally restrained role, and she chooses her moments of release well. It’s been ten years since the “Party Girl” era of Posey’s indie film wrath (a very long ten years), and it’s a delight to see the actress has matured into a far more nuanced adult performer.

“Ohio” asks the world of Posey, putting her in painful moments of martial strife while also asking her to convey the ecstasy and roller coaster buzz of vibrator addiction. Posey rides the role with grace and charm, capturing each lightening bolt of self- discovery while also keeping the role grounded in quietly eroding shame. It’s a sharp bit of acting.

It’s not that “Ohio” falls apart in the last 30 minutes, but more that it ceases to know where it wants go. The late addition of DeVito as Priscilla’s sexual equal is sweet and gentle, but ends up taking the focus away from Jack, who is all but forgotten by the end of the picture. “Ohio” also starts to lose its sense of humor in the mix; it gets to a point where the feature doesn’t actually end, but shuts off suddenly, like a television past bedtime.

I wanted more with these characters, to see where they go as they explore themselves, but Kent doesn’t make time for it, and ends a perfectly swell sex comedy on an abrupt, unsatisfying note that mirrors Priscilla’s predicament all too well.